1//===- FileOutputBuffer.cpp - File Output Buffer ----------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Utility for creating a in-memory buffer that will be written to a file.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Support/FileOutputBuffer.h"
15#include "llvm/ADT/STLExtras.h"
16#include "llvm/ADT/SmallString.h"
17#include "llvm/Support/Errc.h"
18#include "llvm/Support/Signals.h"
19#include <system_error>
20
21#if !defined(_MSC_VER) && !defined(__MINGW32__)
22#include <unistd.h>
23#else
24#include <io.h>
25#endif
26
27using llvm::sys::fs::mapped_file_region;
28
29namespace llvm {
30FileOutputBuffer::FileOutputBuffer(std::unique_ptr<mapped_file_region> R,
31                                   StringRef Path, StringRef TmpPath)
32    : Region(std::move(R)), FinalPath(Path), TempPath(TmpPath) {}
33
34FileOutputBuffer::~FileOutputBuffer() {
35  sys::fs::remove(Twine(TempPath));
36}
37
38ErrorOr<std::unique_ptr<FileOutputBuffer>>
39FileOutputBuffer::create(StringRef FilePath, size_t Size, unsigned Flags) {
40  // If file already exists, it must be a regular file (to be mappable).
41  sys::fs::file_status Stat;
42  std::error_code EC = sys::fs::status(FilePath, Stat);
43  switch (Stat.type()) {
44    case sys::fs::file_type::file_not_found:
45      // If file does not exist, we'll create one.
46      break;
47    case sys::fs::file_type::regular_file: {
48        // If file is not currently writable, error out.
49        // FIXME: There is no sys::fs:: api for checking this.
50        // FIXME: In posix, you use the access() call to check this.
51      }
52      break;
53    default:
54      if (EC)
55        return EC;
56      else
57        return make_error_code(errc::operation_not_permitted);
58  }
59
60  // Delete target file.
61  EC = sys::fs::remove(FilePath);
62  if (EC)
63    return EC;
64
65  unsigned Mode = sys::fs::all_read | sys::fs::all_write;
66  // If requested, make the output file executable.
67  if (Flags & F_executable)
68    Mode |= sys::fs::all_exe;
69
70  // Create new file in same directory but with random name.
71  SmallString<128> TempFilePath;
72  int FD;
73  EC = sys::fs::createUniqueFile(Twine(FilePath) + ".tmp%%%%%%%", FD,
74                                 TempFilePath, Mode);
75  if (EC)
76    return EC;
77
78  sys::RemoveFileOnSignal(TempFilePath);
79
80#ifndef LLVM_ON_WIN32
81  // On Windows, CreateFileMapping (the mmap function on Windows)
82  // automatically extends the underlying file. We don't need to
83  // extend the file beforehand. _chsize (ftruncate on Windows) is
84  // pretty slow just like it writes specified amount of bytes,
85  // so we should avoid calling that.
86  EC = sys::fs::resize_file(FD, Size);
87  if (EC)
88    return EC;
89#endif
90
91  auto MappedFile = llvm::make_unique<mapped_file_region>(
92      FD, mapped_file_region::readwrite, Size, 0, EC);
93  int Ret = close(FD);
94  if (EC)
95    return EC;
96  if (Ret)
97    return std::error_code(errno, std::generic_category());
98
99  std::unique_ptr<FileOutputBuffer> Buf(
100      new FileOutputBuffer(std::move(MappedFile), FilePath, TempFilePath));
101  return std::move(Buf);
102}
103
104std::error_code FileOutputBuffer::commit() {
105  // Unmap buffer, letting OS flush dirty pages to file on disk.
106  Region.reset();
107
108
109  // Rename file to final name.
110  std::error_code EC = sys::fs::rename(Twine(TempPath), Twine(FinalPath));
111  sys::DontRemoveFileOnSignal(TempPath);
112  return EC;
113}
114} // namespace
115